We propose to continue our studies of naltrexone treatment of narcotic addiction with three primary emphases: (1) conditioning factors in addiction; (2) clinical outcomes of naltrexone maintenance: (3) clinical pharmacology of naltrexone. (1) Evidence from controlled studies of humans at this center demonstrated that both positive (euphoric) and negative (withdrawal) reactions to narcotics can be produced as conditioned responses to non-drug stimuli, a phenomenon previously demonstrated only in animals. An experimental program of non-reinforced self-injections (extinction trials) produced dramatic changes in self-injection behavior. We propose to continue to study the effects of modifying these conditioned responses using behavior therapy in conjunction with naltrexone. We will investigate the effects of systematic desensitization of patients to conditioned narcotic effects. Autonomic responses will be monitored and relayed to the patient (biofeedback). These responses will be used to measure the conditioned responses, and insure that patients are not exposed to more potent stimuli until responses to less potent stimuli are extinguished. (2) We propose to continue systematic follow-up studies of outcome in patients maintained on naltrexone, adding two new comparison groups: therapeutic community graduates and outpatients who have successfully progressed from methadone to LAAM therapy and desire drug-free treatment. The effects of variable reinforcement schedules on length of naltrexone treatment will also be systematically studied. (3) We will continue our studies of the efficacy of naltrexone in antagonizing narcotic effects in humans under controlled conditions while monitoring plasma levels.